The invention relates to a filter bag for the reception of filter material, and in particular, to a filter bag for the reception of filter material which is within a casing of a compressed-gas-insulated electric switch unit generating a switch gas jet during a switch-off operation, binds decomposition products from the switch gas.
A filter bag is known, for example, from laid-open publication DE 25 57 298 A1. A three-phase-encased compressed-gas-insulated power switch may be gathered from the laid-open publication. The compressed gas used is sulfur hexafluoride (SF6). By means of an electric arc occurring during switching actions, the sulfur hexafluoride is decomposed. The decomposition products formed occur as gaseous and solid substances. When the concentration of the decomposition products rises, there is the risk that the insulating properties of the compressed gas are adversely influenced. In order to separate these decomposition products and, if appropriate, moisture bound in the sulfur hexafluoride, filters are provided within the casing. The active filter material is introduced in small filter bags into the interior of the casing. To receive the filter bags, reception devices are provided inside, which include, for example, a metallic perforated material, in order to achieve good gas permeability. Arranging the reception devices for the filter bags within the casing arises from the requirements of sufficient dielectric and thermal dimensioning. The reception devices, in addition to receiving the filter material bags, serve essentially for protecting the filter bags against hot switch-gas or plasma streams occurring during a switching operation. The deflector action of the perforated material is necessary in order to avoid combustion of the filter bags and consequently destruction of the filters. The design of the perforated material must in this case be such that a sufficient throughflow is possible in spite of the protection of the filters.
The arrangement of the filters always constitutes a compromise between a position with an optimum filter behavior and a favorable electric arrangement of the reception devices influencing the electric field.
The present invention discloses a filter such that a reduction of metallic reception devices is obtained within compressed-gas spaces of electrically encased installations.
In one embodiment of the invention, the filter bag includes a high-temperature-resistant fabric and is arranged in the switch gas jet. When the filter bags are produced from a high-temperature-resistant fabric, it is possible to dispense with metal sheets which protect the filter bags against the hot switch gases. With these metal sheets being dispensed with, they can no longer influence the dielectric field within the casing. The filter bags can then be arranged within the casing in a substantially more flexible way. Furthermore, an appreciable cost benefit is to be noted, since the complicated reception devices have a simpler configuration or other subassemblies can be designed in such a way that the reception devices are dispensed with completely.
Furthermore, there may be provision for the fabric to be a mixture of amorphous, inorganic and high-crystalline organic synthetic fibers.
A fabric of this kind has good gas permeability and consequently has an insignificant influence on the filter action of the active filter material. In particular, the continuous-duty temperature resistance of several 100xc2x0 C. and the contact temperature resistance of more than 1000xc2x0 C. constitute beneficial properties for use within a compressed-gas-insulated switch installation. Furthermore, the material is resistant to sparks, flames and smoldering. In addition to the excellent thermal properties, a fabric of this kind has optimum mechanical properties, in particular a high tearing strength in the longitudinal and transverse direction, thus ensuring good protection of the filter material against mechanical stress during introduction into the casing and against mechanical vibrations occurring during operation. Fabrics of this kind are known, for example, under the tradenames Systaceram or Kevlar.